Abstract

Background

The use of insecticides to control malaria vectors is essential to reduce the prevalence
of malaria and as a result, the development of insecticide resistance in vector populations
is of major concern. Anopheles arabiensis is one of the main African malaria vectors and insecticide resistance in this species
has been reported in a number of countries. The aim of this study was to investigate
the detoxification enzymes that are involved in An. arabiensis resistance to DDT and pyrethroids.

Methods

The detoxification enzyme profiles were compared between two DDT selected, insecticide
resistant strains of An. arabiensis, one from South Africa and one from Sudan, using the An. gambiae detoxification chip, a boutique microarray based on the major classes of enzymes
associated with metabolism and detoxification of insecticides. Synergist assays were
performed in order to clarify the roles of over-transcribed detoxification genes in
the observed resistance phenotypes. In addition, the presence of kdr mutations in the colonies under investigation
was determined.

Results

The microarray data identifies several genes over-transcribed in the insecticide selected
South African strain, while in the Sudanese population, only one gene, CYP9L1, was found to be over-transcribed. The outcome of the synergist experiments indicate
that the over-transcription of detoxification enzymes is linked to deltamethrin resistance,
while DDT and permethrin resistance are mainly associated with the presence of the
L1014F kdr mutation.

Conclusions

These data emphasise the complexity associated with resistance phenotypes and suggest
that specific insecticide resistance mechanisms cannot be extrapolated to different
vector populations of the same species.